Pinger,
I don't often say this, but I'm at my wit's end, too. I have been testing all this between my MBP, booted in Vista, and another Mac running Leopard here. My success has been limited and inconsistent.
In other words, I'm not sure a reinstall is going to help you. It is true that now would be the best time to perform one, and I heartily recommend doing so for anyone with a new computer, since many computers (Macs or otherwise) ship from the factory with incipient disk errors. For new Mac users, doing so comes with the additional benefit of introducing them to the process, thereby immediately increasing their knowledge and understanding of OS X.
If you do jump into this, know that it is
way easier than doing the same in Windows. Anecdotally, when I installed Windows for the first time on my MBP this past December, I was struck by how
barbaric, complicated, and slow it was, even with Vista. You will have several options when formatting (erasing) and reinstalling, but this is the route I recommend you take:
1) Boot to the "Software Restore" DVD that came with the Macbook. Insert the disk with the computer running, then restart. When you hear the startup chime, immediately hold down the "C" key, and continue holding it down until you see the Apple logo.
2) Once the installer loads, you must choose a language. Do so, then look in the Menu Bar (at the top of the display) for the "Utilities" menu. Open Disk Utility from this menu. This is the same Disk Utility that you (or your daughter) will eventually use in OS X. In the "source list" on the left, you will see "devices" (physical hard drives, optical drives, etc.), with "volumes" indented beneath the device that stores them. Certain tasks can only be performed on a device, others on only volumes, while some tasks are common to both. I mention this, because I want you to select the entire internal hard drive (the "device"), not the named volume that will appear indented underneath.
3) With your hard drive selected, switch to the "Erase" pane in the body of the window. Find and click on the "Security Options..." button. This will open a drop-down "dialogue sheet." Enable the option to "Zero All Data." This tells Disk Utility to write zeroes to the entire surface of the drive, instead of performing a simple erasure. This adds a considerable amount of time to the process (an hour or more), but it brings the added benefit of scanning for and "mapping out" any bad blocks that may exist on the drive. Your chances of having a bad block are not terribly high at this time, but the risk does exist, and this is good insurance for the immediate future. Click "OK" to dismiss the dialogue sheet.
4) You can give any name you like to the volume that will be created during the format, but it will probably be easiest to keep the same default name (Macintosh HD). This can be changed at any later time. Enter the new name in the appropriate field, then click "Erase." Wait for the process to complete.
5) When the drive has been formatted, quit Disk Utility to return to the installer. Proceed through the installer, following the clear instructions it will provide, until you reach the final screen that includes a "Customize..." button. Here, you can jettison some of the normally unwanted "fluff" that is installed by default with OS X. The interface is self-explanatory; simply check those items you want to keep, and uncheck those that you will not need. I recommend you opt out of any "Additional language translations" that you think you will not need (most users will not need to use their computer in Korean, for example). This will save oodles of disk space. Similarly, you can choose not to install drivers for printers you
know you will not use (be careful here, as one never knows...). Any "test drive" packages are usually unwanted, too. If in doubt on any item, it is best to install it.
6) When you have made all your choices, proceed with the installation. Follow the on-screen prompt to insert the second disk when it appears. At the end of the installation, you will enter the "Setup Assistant, just as you did when you first started the Macbook.
7) Instead of using "Software Update," download the
10.5.3 "Combo" update. This will bring you right back up to speed with a single, large download, instead of several "delta' downloads. Once you have run the "Combo" and restarted, you can use Software Update to tie up any loose ends.
As I have already mentioned, I'm not sure that this is going to provide any relief as far as Mac-PC networking is concerned. However, it just might, and it is one thing that I usually recommend as a matter of course for any new computer anyway. If this does solve some problems, please let us know. Since I and others are having the same problems with cross-platform sharing, any success you have with starting from scratch and using the "Combo" updater (which is known to be sometimes less error-prone) could help many others.
Scott